Airplane navigating apparatus



F. M. POTTENGER, JR., E-r AL 2,070,178

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AIRPLANE NAVIGATING APPARATUS Filed June 6, 1954 8 Sheets-Sheet 2 Feb.9, 1937. F. M. POTENGER, JR., TAL 2,070,178

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y 2/9 04 226 f 2 /z Patented Feb. -9, 1937 2,070,178 AmPLANE NAVIGATINGAPPARATUS Francis M. Pottenger, Jr., Monrovia, and James R. Balsley, LaCanada, Calif.; said Balsley assignor of twelve and one-half per cent toPaul Whittier and twelve and one-half per cent to Keith Scott, both ofLos Angeles, Calif.

Application June 6, 1934, Serial No. 729,216

22 Claims. (Cl.- 250-11) ICE Our invention relates to devices forascertaining the position of one point'in space with respect to a secondpoint, having special reference to such devices incorporated innavigation apparatus, and is directed particularly to an automaticposition-indicating system involving calculationby triangulation andproviding guidance for the safe landing of aircraft under conditions ofsubstantially no visibility.

The application of such a device to blind iiying involves numerousdimculties, the solution of which demonstrates certain objects andadvantages of our invention as will become apparent in our laterdetailed description.

In general, the requisites of such apparatus for successful applicationto airplane navigation are: iirst, that the apparatus be independent ofweather and light conditions; second, that the apparatus be accurateWithin certain limits and be absolutely dependable; third, that theapparatus function with sufficient rapidity to keep pace with the`continuous change in location of Va speeding airplane; fourth, that theapparatus be fully automatic, requiring no manipulation or adjustment bythe pilot; and, fth, that the apparatus include a visual indicator thatWill clearly and conveniently reveal the position of the airplaneeitherin units of distance from the landing field and altitude above theground or reveal graphically the relation of the planes position to adesired line of approach to the landing 4 eld, or both.

' our system, and, in addition, we have providedA than mechanicalinterlocking connections; and.. we have entirely eliminated the humanequation from the functioning of the device.-- These provisions all havea bearing on the dependability of for modulating the infra-red rays andmaking our apparatus selectively responsive to the modulated rays inorderto avoid any possibility of interference from infra-red raysextraneous to our system.

Our apparatus keeps pace with the rapidly changing factors involved,because it functions electrically rather than mechanically.

To meet the fourth requirement, the characteristic of being automatic,in a system of measuration by triangulation involving electro-magneticradiation, we have provided pointers that will automatically be trainedon the source of the radiation and have further provided automatic meansfor deriving the distance in question from the angular positions ofthese pointers. We have made the pointers automatic by associating withthem photoelectric cells having circuits selectively responsive to theelectro-magnetic radiation, and we have provided automatic calculationby utilizing certain characteristics of electric circuits, as will bemore fully disclosed hereafter.

Finally, the position continuously reckoned by iour apparatus iscontinuously indicated to the pilot in a manner that reveals not onlythe altitude of the airplane and the distance from the airport, but alsoreveals the relation of the planes position to a desired line ofapproach to the airport.

The objects and advantages of our invention,

`indicated by the above summary, will become more apparent in thedetailed description to follow, as will certain other featuresillustrated by our preferred embodiment of the invention.

In the accompanying drawings:

Fig. 1 diagrammatically represents the plan view of an airplaneapproaching a beacon at an airport;

Fig. 2 diagrammatically represents the side view of an airplaneapproaching a beacon at an airport;

Fig. 3 is the front elevation of a pointer, with its associatedphotoelectric eye;

Fig. 4 is a plan view of Fig. 3;

Fig. 5 is a central longitudinal section taken as indicated by the line5-5 of Fig. 4;

Fig. 6 diagrammatically presents the arrange-` ment of quadrant cathodesin a photoelectric eye;

Fig. 'l is a diagram representing the outer lens of the photoelectriceye divided into quadrants for the purposes of description;

Fig. '7a. is an enlarged central portion of Fig. 7;

Fig. 8 is a schematic arrangement of our system, showing theinter-relationships of the moving parts and the electric circuitsinvolved;

Fig. 9 is a simplified diagram of certain circuits in Fig. 8;

Fig. 10 is a suggested arrangement of the indlcating instruments on apanel or chart:

Fig. 11 is the side elevation of a typical resistor employed in ourapparatus;

Fig. 12 is a transverse section taken as indicated by the lines |2-I2 ofFig. 11;

Fig. 13 is the side elevation of a resistor arranged vfor compensatingmovement; 5 Figs. 14, 15 and 16 are diagrams of circuits arranged forcalculation by voltage measurements;

Figs. 17 and 18 are diagrams of circuits arranged for calculation bycurrent measurements; Fig. 19 is a diagram of a circuit for calculation10 by both voltage and current measurements;

Fig.- 20 is4 a diagram of an electrical arrange-v ment for ground speedindication;

Fig. 21 indicates the arrangement of cathodes in a second form ofphotoelectric eye in a pointer 15 construction;

Fig. 22 is a diagram of the outer lens of the eye as divided intosectors corresponding to the cathodes of Fig. 21;

Fig. 23 is a wiring diagram of the circuits in- 20 volved in this secondform of pointer;

Fig. 24 is a plan view of a third form of pointer involving two armshere shown spread apart;

Fig. 25 is a similar View showing the two arms closed together in theirnormal positions;

Fig. 26 is a longitudinal section through Fig. 25;

Fig. 27 is a fragmentary transverse section taken as indicated by line21-21 of Fig. 25;

Fig. 28 is an enlarged view of a switch construction in this third formof pointer;

Fig. 29 is a wiring diagram showing the circuits used in this third formo eye; and

Fig. 30 is a diagram suggesting, as viewed from the front, thedisposition on the airplane of three of this third form of pointer.

In applying our invention to the problem of navigating an airplane, wehave the choice of establishing our base for triangulation either on thelanding eld or on the plane. The principal advantage of having the baseon the landing field 40 's that such a base may be of relatively greatextent compared to a base established on the plane, with consequentgreater permissible variation from absolute accuracy on the part of thecalculating apparatus. One disadvantage of a base on 45 the minding newarises from the fact that with changing wind conditions the airplanemust approach the landing field from different directions, so that, ifbut one base is established on the field, the relation of the line ofapproach of 50 the airplane to that base is not the same for eachdirection of approach. Such difficulties may be .met by providing for aselection of bases on the landing neld, or by providing for adjustmentsin the computing apparatus of the airplane to 55 be made in accordancewith the direction of approach. We prefer, however, to establish thebase of triangulation at the airplane, so that only one radiating beaconis required at the airport. Figs. 1 and 2 indicate the relationsinvolved in 60 the approach of an airplane having such a base line, to asingle beacon on the landing field. n

the airplane, generally designated 20, are two pointers, L and R, theposition of which and alignment of which with respect to beacon N arein- 65 dicated by dotted lines 2l and 22. In Fig. 2, dotted line 23represents either or both lines 2| and 22 of Fig. 1. Beacon N maygenerate any type of electro-magnetic radiation, but, for the4 purposesof the preferred form of our invention,

70 we contemplate employing quasi-optical waves,

as, for example, an infra-red wave-length of approximately ten thousandangstrom units, and we further contemplate modulating to one hundred percent (100%) such' .radiation with some de- 75 sirable frequency, as vehundred (500) cycles per second. By arranging the eyes to be selectivelyresponsive to such modulation, we avoid interference by stray infra-redradiation extraneous to our system.

The construction of pointers L and R, may be understood by reference toFigs. 3 to 5. For each pointer-a base plate 24 is fixed to the wing ofthe plane, with its longitudinal axis parallel with thelongitudinal'axis of the ship. The front end of the base plate supportsa vertical bearing, generally designated 25, and afllxed to andsupported by the rear of the base plate is an encased motor 26. Ahorizontally movable turntable 21 is pivotally supported in parallelspaced relation to the base plate by bearing 25 and a series of steelballs 28 that are retained in a ball race 29 formed by complementaryarcuate grooves in the turntable and base plate, respectively. Toprevent the two parts from separating unduly, headed pin 30, fixed tothe under side of turntable 21, extends through a suitable arcuate slot3l in base plate 24.

The rear edge of turntable 21 is provided with an arcuate rack 32concentric to bearing 25, the teeth of the rack being engaged by wormgear 33 driven by motor 26. Mounted on turntable 21, near the rear, is asecond motor 34. Integral with the forward portion of the turntable is avertical pair of standards 35 presenting horizontal bearings 35a, theaxis of these bearings intersecting the extended axis of verticalbearing 25. An underslung cradle 36, pivotally supported by bracket 35,is provided with a vertically disposed arcuate rack 38, the teeth ofwhich are .engaged by worm gear 39 driven by motor 34.

A globular photoelectric eye 40, having a base portion 4|, is supportedon cradle 36, with its spherical center coincident with the aforesaidintersection of the horizontal pivotal axis of the cradle with thevertical axis of pivot bearing 25 of the turntable. It will be notedthat by virtue of the described arrangement the center of the sphericalphotoelectric eye is the pivotal point for movement in two planes, andthis assemblage may be considered, therefore, as, in eiect, a pointerpivoted for universal movement about said center, the axis of thepointer being an imaginary line :r- (Fig. which line is also thelongitudinal axis of photoelectric eye 40. Motor 34, through worm gear39, controls the disposition of this pointer through vertical arcs andmotor 26, through worm gear 33, controls the angular disposition of thepointer through horizontal arcs. Preferably, one revolution of motor 26produces thesame degree of angular displacement of the pointer as iscaused by one revolution of motor 34, such provision being made bydesigning worm gear 33 as a double-pitch screw and worm gear 39 as asingle-pitch screw.

Mounted on the front of photoelectric eye 40 is a lens cylinder 42,coaxial with line :xx-rc, incorporating lens 42a. and a lter or lightscreen (not shown) excluding all but a narrow band of the selectedelectromagnetic radiations. The photoelectric eye itself comprises, ineffect, a plurality of photoelectric cells in a single bulb, there beinga ring-shaped plate or anode indicated at 43, common to all the cells.and four separate cathodes 44, each being a semi-spherical quadrant inthe rear hemisphere of eye 40, as indicated in Figs. 5 and 6. Thesequadrants or sectors are insulated from each other by spaces or avenues45, the arrangement of the four cathodes being as shown in Fig. 6. Itwill be noted that these avenues intersect on axis @-2, so

"42 may be considered as divided into four quadrants, I', 2', 3', and4', respectively, as indicated in Figs. 3 and 7. The four cathodes, orcells, 44 will be considered as having correspond- Ving numbers I, 2, 3and 4, the numeral of the cell corresponding to the quadrant of thefront lens through which light passes and eventually falls upon thecell. Obviously, the numerical arrangement of the cells will depend uponthe type of lens system used. If a single convex lens is employed, thenumerical arrangement of the cells Will be as indicatedrin Fig. 6. Wherein the appended claims the position oi a cell is given relative to theaxis of the pointer, it will be understood that reference is made to theapparent position of the cell indicated by I', 2', 3', or 4 in Fig. 7.

Cathodes 44 are` of a material such as thalophide, having maximumsensitivity at 10,000 angstroms. It is also a requisite of the lenssystem that the electromagnetic radiations passed therethrough befocused to a sharp image point or circular spot of substantiallyunvarying magnitude as the airplane approaches the beacon.

The manner in which a photoelectric eye and the associated mechanismsmay serve automatically to train the pointers L and R continuously uponbeacon N will now be explained. The terms upward", downwardright andleft, used to ydescribe movements of the pointer, will be understood asmovements having such appearance to an observer facing the pointers fromthe front. It will be apparent, then, that because of the disposition ofthe photoelectric eye with respect to its associated pointer, when animage is projected on cathode or cell quadrant I (quadrant of the lens),thereby energizing the photoelectric circuitv through that particularcell, the pointer should react by moving upward to the left, in adirection tending to center the image at neutral square 46, therebytraining axis :v of the pointer on the distant beacon. The arrangementof apparatus associated with the two pointers for providing suchreaction to radiations from the distant beacon is set forthschematically in Fig. 8.

Each individual photoelectrlc cell, distinguished by a quadrant cathode44, controls a separate input circuit, the 'description of one of whichwill suftlce for all.4 For example, consider cell I of the left wing.'Ihe input circuit may be traced as follows: cathode I, wire 41, bandpass illter comprising condenser 48 and two parallel tuned circuits 49,wire 58, ground 5|, ground 52, battery 53, wire 54, and ring plate oryanode 43,

vpreviously mentioned. This circuit is tuned and filtered to themodulation frequency 500 cycles and controls the potential of grid 55 inamplifying vacuum tube 56.

Tube 56 is a heater type, having heating element 51 energized by asuitable source conventionally indicated at 58, the energizing circuitby condenser 63. Grid 55 controls the output or Y plate circuit, whichmay be traced as follows: plate 64, wire 65, solenoid coil of relay 66,wire 61 wire 68, source of current conventionally indicated at 69,ground 18, ground 5|, wire 58,

resistor 62 and tube cathode 6|. Relay 66 is normally open, i. e.,open'when de-energized.

It is apparent from this arrangement that when cathode 6| is energizedby the focused infra-red image modulated at the selected frequency, analternating current voltage of the modulation frequency will bedeveloped across tuned circuits 49 and the plate current of the tubewill be increased suciently to close relay 66.

In like manner, photoelectric cathode 2 is associated with vacuum tube1| and normally open relay 12; photoelectric cathode 3 is associatedwith tube 13 and normally open relay 14; and photoelectric cathode 4 isassociated with tube 15 and normally open relay 16.

Numeral 11 indicates the armature of shuntwound motor 26 associated withhorizontal movements of the left pointer L. The ileld winding of thatmotor, generally designated by the numeral 18, is center-tapped to oerthe choice of a rightpropelling electromagnetic ileld or aleft-propelling fleld, the two halves of the eld winding being, ineiect, independent, thereby providing means to` reversibly control therotation of armature 11. In the same Way, armature 19 of shuntwoundmotor 34 controlling the vertical position of the left pointer isreversibly controlled by similarly tapped field winding, generallydesignated 88.

A source of electromotive force to energize the motors is indicatedconventionally at 8|. The circuit through armature 11 may be traced:source 8|, wire 82, wire 83, wire 84,' either relay or relay 86, Wire81, armature 11, Wire 88, wire 89, wire 98, back to source 8|. Aparallel circuit through armature 19 may be traced as follows: wire 9|,branchingirorn wire 83, either relay 92 or 93, Wire 94, armature 19, andwire connecting with wire 89.

The circuit through the right propelling eld of motor 26 is: source 8|,wire 68, wire 89, wire 96 to the center tap of eld Winding 18, theright-propelling half of field winding 18, wire 81, solenoid coil ofrelay 85, wire 98 through either relay 12 or relay 16, wire 99, thenceto Wire 83 on the other side of source 8|. The circuit through the leftpropelling eld is: wire 96 to the center tap of field winding 18, theleft-propelling half of eld Winding 18, wire |88, solenoid coil of relay86, wire 8| through either Arelay 66 or relay 14 to wire 99 on the otherside of source 8|.

The circuit through the upward propelling field is: wire |82 branchingfrom wire 89, center tap of eld winding 80, the up-propelling half offield Winding 88, wire |83, solenoid coil of relay 92, wire |84, eitherrelay 66 or relay 12, to wire 99 on the other side of source 8|. Thecircuit through the downward propelling field is: wire |02 to center tapof eld winding 88, the down-propelling half `of field winding 88, wire|85, solenoid coil of relay 93. wire |86, through either relay 14 orrelay 16 to wire 99 asbefore.

Relays 85, 86, 92 and 93 are normally closed and open only whenenergized.

In the other half of Fig. 8 the parts corresponding to the aboveenumerated elements are correspondingly situated and need not berecited. Armature |88 controls the vertical movement of pointer R, andarmature |89 controls the horizontal movement of that pointer.

'I'he functional relation of a photoelectric eye` to its associatedpointer vmay be understood by describing the effect of an infra-redimage at the selected modulation cast upon quadrant I of left eye L. Toavoid confusion arising from any inversion in the order of the quadrantson the four cathodes with respect to the order of the quadrants on thefront lens, the path of the image will be described with respect to thereceiving quadrants I, 2', 3', 4' on the lens, as may be understood byreference to Fig. '7.

When the infra-red image spot appears on quadrant I of the lens at theposition III) (Fig. 7), cathode quadrant I thereupon becoming activateddischarges electrons that are attracted by anode 43 of the photoelectriceye. This action closes the input circuit associated with tube 56, whichtube thereupon serves as an amplifying relay to close the circuitthrough the solenoid coil of relay 66, closing the relay. The closing ofrelay 66 energizes the up-propelling half of field Winding 80 associatedwith armature 19, and also energizes the left-propelling half of lleldwinding 18 associated with armature 11. The simultaneous movements ofthese two armatures move the eye upward and to the left so that the pathof the image is a-component of those two movements, the image movingdiagonally, as indicated by dotted line I I I. When the image spot hasmoved diagonally sulciently to encroach upon quadrant 2 of the lens, asindicated at II2, cathode 2 also is energized, causing relay 12 toclose. Both sides of field coil 18 are now energized and, being opposed,cancel each other as far as they affect armature 1-1. Since both relays85 and 86 are now energized, the circuit through armature 11 is broken.Rotation stops in armature 11 of motor 26, but continues in armature 19of motor 34, so that the image spot now moves vertically downwardasndicated by dotted line II3. When the image arrives at the exactcenter of the lens, as indicated at II4, it bridges all four quadrants,thereby causing all four relays 66, 12, 14 and 16 to close and relays85, 86, 92 and 93 to open, stopping-movement of pointer L. At thisposition, pointer L is trained on beacon B. The same result will beattained if the image when centered clears all the quadrants orencroaches upon none of the quadrants suiciently to operate any ofrelays 66, 12, 14 and 16.

It has been indicated above that when the imageis centered on neutralsquare 46, the cathodes should be balanced, i. e., either that all fourmotor relays 66, 12, 14 and 16 be open, or that, as

1 an alternate situation, all four said relays 'le closed, and that whenthe image shifts slightly energized suiliciently to close, then thediameter of the image should be approximately that of circle IIS. If theimage is slightly less In diameter than this circle, then the image atdead center will cause none` o-f the relays to be actuated, and, ifshifted from dead center, will cause one, or not more than two, relaysto be actuated.

If, on the other hand, the image diameter is slightly greater than thatof circle I I5, the image at dead center will cause all four relays tobe actuated, with the result that neither of the associated motors willbe energized, and when the slightly oversized image shifts from deadcenter, three of the four relays will be opened. If the image is madetoo large, however, it may be possible for the image to shift diagonallyfrom dead center without vdeenergizing more than one relay, in whichcase the motors do not respond. Because of this possibility, it isadvisable to focus the image at slightly less than the diameter ofcircle H5. Preferably, the image will be reduced to what is virtually apoint, the avenues being correspondingly narrow. Obviously, the problemof accuracy is simplified by focusing to a minute image. Absolutecontrol of the size of the image may be accomplished by using an irisdiaphragm within the lens system.

From the above description, the automatic action of the pointers will beunderstood, the image of the beacon, in effect, seeking the center ofthe photoelectric eye that is xed to the pointer. It will be noted thatarmature 11 rofates indirect proportion to the right and left movementsof the left eye or pointer, and armature 'I9 moves in direct proportionto the up and down movements of the left eye or pointer; armature |08moves in direct proportion to the up and down movements of the right eyeor pointer; and armature |09 rotates in direct proportion to the rightand left movements of the right eye or pointer.

There remains the problem of deriving the distance to the airport andthe altitude of the airplane from the angular positions of the twopointers as represented by the rotary positions of their associatedarmatures.

An equation or formula for computing distance by triangulation involvesa minimum of three factors in the case of an oblique triangle, or twolfactors in the case of a right-angle triangle, and

one of these factors must be a side of the triangle. In the presentarrangement, when the airplane approaches the beacon, one of thesefactors, the base line, represented by the distance between thepointers, is constant, while the other factor or factors arecontinuously variable.

Any of the formulas for triangulation may be employed. If, for instance,the right pointer, while trained on the beacon, is perpendicular to thebase line B, as shown in Fig. 1, the distance to the beacon measuredalong the axis of the right pointer will equal B tan p being the angleof the left pointer with respect to the base line. In such acalculation. there is only one variable, angle If one' of the pointersisnot perpendicular to the base line, a formula involving two variablesis necessary.

After the distance has been derived, the altitude of the airplane can becomputed from the angular position of one of the pointers with respectto the horizontal. In Fig. 2, for instance, Athe distance D and anglebeing known, the altitude H=D cos We contemplate solving such equationsby electrical means associated with the two pointers. In doing so, wehave the choice of utilizing either the'voltage characteristic or thecurrent characteristic of an electric circuit, or both characteristics.In the preferred form of our invention we utilize the voltagecharacteristic, in a manner that will now be explained.

Eig. 14 shows a potentiometer in which resistor |20. shunts battery I2I.A voltmeter |22 is in series with one terminal of resistor |20 and amovable resistor contact conventionally indicated at |23. A stop |24limits the movement of contact |23 at a minimum voltage corresponding tothe logarithmic value of a constant which is to be electricallymultiplied by a variable. That portion of resistor |20 over whichcontact |2315 free to range is wound to vary in accordance with thelogarithmic value of the said variable. The voltage registered byvoltmeter |22 will represent the sum of these logarithmic values, and,if the ,voltmeter have a suitably calibrated logarithmic scale, thenumerical product of the constant and the variable may be ascertaineddirectly from the position of the indicating needle of the voltmeterwith respect to that scale.

Fig. 15 represents a similar arrangement, in which contact |25a is freeto traverse the length of resistor |25, the minimum voltage thatrepresents the constant involved in the equation being supplied byauxiliarybattery |28 in series with voltmeter |21.

The arrangement shown in Fig. 16 provides for multiplying two variablefactors by a constant. Resistor |28, wound-to vary as the logarithmicvalue of one factor, bridges battery |29 and is traversed by movablecontact |30. In like manner, resistor |3| wound to vary as the logarithmof the second variable, shunts the terminals of battery |32 and istraversed by a second contact |33. A third battery, |34, having itsterminals connected .respectively to the lower ends of resisters |28 and|3|, has a voltage corresponding to the logarithm o f the constantinvolved. Volt# meter |35, calibrated to-indicate the product of thethree factors, has one terminal connected with contact |30 and thesecond terminal connected with contact |33,'so that it is in series withbattery |34 and variable portions of resistors |28 and |3|.

Figures 14, 15 and 16 are offered to illustrate the principles ofcalculation by electric circuits. How these principles may be applied toour specific problem, as contemplated in the preferred form of ourinvention, may be understood by considering Fig. 9 together with Figs. 1and 2. f

Resistor |38 of Fig. 9, wound to vary in accordance with the logarithmictangent of an angle, shunts battery |31, and is traversed by a movablecontact |38. Contact |38 is controlled by movements of ,pointer L withrespect tobase line B lower end of resistor |36 are voltmeter |39 and abattery |40,` having a voltage corresponding to the logarithm of baseline B. From the foregoing explanation, it will be clear .that ifpointer R, of Fig. 1, is perpendicular to base line B, voltmeter i39,having a properly calibrated logarithmic scale, will indicate theinstant value of distance D.

A second resistor |4|,wound to vary as the logarithmic cosine of anangle, shunts the terminals of a third battery |42 and is traversedbymovable contact |43. Contact |43 is controlled by vertical movements ofeither pointer L or pointer R. One terminal of' a second voltmeter |44is connected with contact |38, and the second terminal is connected withcontact |43, with the result that the indicating needle of voltmeter`|44 will take a position corresponding to the voltage registered byvoltmeter |39 plus a voltage corresponding to the logarithmic cosine ofangle This second voltmeter is calibrated to give the instantaneousvalue of altitude H in Fig. 2.

For the purpose of indicating to the pilot of the airplane the deviationof pointer R from the desired disposition perpendicular to base line B,one of the three batteries, for instance battery |42, may be shunted byresistor |45l the resistor being the usual type wound to vary linearlyand being traversed by a movable contact |46. Contact |48 is controlledby horizontal movements of pointer R. Voltmeter |41 is in series withcontact |46 and one end of resistor |45. This third voltmeter is socalibrated that at a given point, as, for instance, the midpoint ofresistor |45, pointer R is 90 from base line B and the indicating needleshows zero deviation.

It is apparent that if contact |38 is suitably connected with pointer L,or the mechanism associated with the horizontal movement of pointer L,contact |43 connected to either pointer, or the mechanism controllingthe vertical movement of Veither pointer, and contactY |46 properlyconnected with pointer R, or the mechanism controlling the horizontalmovement of pointer R, the system will function automatically, voltmeter|39 indicating the distance to the beacon, voltmeter |44 indicating thealtitude of the airplane, and voltmeter |41 indicating the deviation ofthe flying axis of the ship from the line of approach necessaryV fortriangulation involving a right triangle.

The circuit shown in elementary form in Fig. 9 may be recognized in theschematic arrangement of Fig. 8, corresponding numbers indicatingcorresponding parts. Dotted line |48 indicates an operative connectionbetween armature and contact |38; dotted line |49 indicates an operativeconnection between armature |08 and contact |43; and dotted line |50likewise indicates an operative connection between armature |09 andcontact |48.

How the pointers may be mechanically associated with the variousresistors, may be understood by considering the construction of atypical resistor as illustrated in Figs. l1 and 12. Resistor form woundtransversely with wire |5| is supported at each end by spaced standards|52, the assembly being reinforced by two spaced rods |53 fixed to thestandards above and parallel with the top edge of form |5|. Form |5| maybe of any suitable insulating material, preferably of sheet material,such as fibre board. Wire |5|a is of uniform resistance, and, if it isdesired that the resistor vary linearly in resistance, the upper andlower edges of the form will be parallel. If, however, the resistance isto follow the values of a variable. the lower edge of the form will becut to follow the curve of the variable, as indicated by Fig. 1l.

Journalled in standards |52, parallel with the top edge of form |5|, isa worm or screw |54 operatively connected, as by coupler |55, with ashaft |56 of one of the four armatures. Screwthreadedly engaging screw|54 and slidingly engaging rods |53 is a carrier |51, from which one ormore contacts |58 extend downward to slide upon the windings of resistorwire |5|a. Obviously, since the pointer associated with a givenvarmature and the contact carrier |51 are both Vlarge as 4necessary toobtain accurate changes of resistance commensurate with small changes inthe angular position of the pointer.

Fig. 13 -shows a modication of such a resistor to provide forcompensating movements of the resistor winding as required, forinstance, in resistor |4| of Fig. 8. Angle in Fig. 2 is measured fromthe true vertical; therefore, resistor |4| must have a fixed relation tothe vertical regardless of the inclination of the ship. Therefore,resistor winding |4|, is movably mounted and controlled by suitablemeans such as a gyroscope, pendulum, or other similar device. Theresistor shown in Fig. 13 is similar to that shown in Figs. 11 and l2,identical parts having corresponding prime numbers, but resistor` form|59 is slidably mounted in brackets |52' and is 0poperatively connectedwith some vertical-seeking device (not shown), as by pivotally connectedrmi |60.

The voltmeters may be' simply independent in- .dicating devices on apanel, as shown in Fig. 8,

or the indicators may be mounted on a panel or calibrated chart |6|(Fig. 10). Such a chart graphically indicates the position of the ship.Voltmeter |39 on one side of the chart has an indicating needle |6 2positioned totraverse a `distance-reading scale |63. Similarlypositioned on the opposite edge of the chart is Voltmeter |44, havingits indicating needle |64 movable along altitude-reading scale |65.

The position of the intersection of needles |62 and |64 relative tochart |6| will vary with thel position of the airplane in space, and,obviously, lines may be drawn on the chart to aid in the visualizationof the position of the airplane in space. For instance, a line |66 maybe drawn to correspond to the movement of the intersection of the needleacross the chart, as the airplane follows a desirable gliding angle orline of optimum glide to the landing i-leld (no signincance is to beattached to the specific disposition of line |66 in Fig. 10) By such anarrangement the aviator can be informed continuously of his position inspace relative to such a line of optimum glide, as well as his positionrelative to the beacon. It will be noted that the accuracy of our systemincreases as the beacon is approached.

The third Voltmeter |41 may be arranged at the bottom of chart |6| withits indicating needle |61 having a normal vertical position at themiddle of a scale |68 calibrated in degrees of deviation from thedesired course. Such an arrangement has the advantage of confining thepilots attention to a relatively small area on the chart, and revealsthe maximum amount of information at a glance.

The resistors may be standard, battery |40 and the calibration of theVoltmeter varying with the base line that a given airplane canaccommodate.

The operation of the preferred form of our invention will be readilyunderstood from the foregoing explanation. As the airplane approachesthe desired airport, pointers L and R are automatically trained on thebeacon at the airport, and the lelectrical arrangement describedcalculates the instant position of the ship in distance to the airportand altitude above the ground. The calculations are continuously andautomatically corrected to give the successive instant positions of theship, such corrections being made at a rate commensurate with the yingspeed of the ship. The photo-electricy eyes respond only to infra-redrays, and only to intersection of the needles moving along line |66advises the pilot of his approximate speed and his distance from thelanding eld. It will be obvious that where the beacon itself is at asubstantial elevation above the ground, scale |65 associated with needle|64 and the disposition of line |66 may be arranged to compensate forsuch elevation.

The specific form of our invention selected for the purposes ofillustration and disclosure suggests a Wide range of possible changesand structural modifications, and we reserve the right to all suchchanges and modifications that properly come within the scope of ourappended claims.

For instance, our invention may be arranged to utilize the currentcharacteristics of an electric circuit for the purpose of calculatingthe position of the airplane automatically. In view of our disclosureabove, such a modification may be understood by considering diagramsgiven in Figs. 17 and 18. A

L and R are pointers corresponding respectively to L and R of Fig. 1.Pointer R' controls, as by arm |69, movable winding |10 of a resistor.Pivoted to the same axis as arm |69 is a right-angle bell crank havingarms |1| and |12, arm |1| being connected as by link |13 or other meanswith pointer L', so that pointer L and arm |1| are always parallel. Byvirtue of this arrangement, the angle between arm |69 and arm |12 willalways be equal to angle at beacon N, and contact |14 on arm |12 willmeasure on winding |10 a distance corresponding to the magnitude ofangle Operatively connected with pointer L is a movable contact |15associated with a fixed resistor |16, the resistor being taped at anintermediate point |11 and being free at the ends. The base line forcalculation by triangulation is represented by dotted line B' and thearrangement is such that when pointed L' is perpendicular to line B',contact |15 is at tap |11 of resistor |16.

The formula to be used here for the distance measured along one lengthof the triangle is distance D=B' sin 0 cosec or log D=log B'+log sin@-l-log cosec 'I'he electric circuit may be traced as follows: contact|15, wire |18, battery |19, wire |80, limiting resistance IBI, wire |82,contact |14, resistor |10, wire |83, ammeter |84, Wire |85, and resistor|16. When both pointers are trained ninety degrees from base line B', nopart of either resistor Winding |16 or resistance winding 10 is includedin the calculating circuit, at which positions of the pointers thecurrent in the circuit as determined by battery |19 and the resistanceof the circuit plus limiting resistance |8| will correspond in value tothe logarithm of approximately the maximum distance from the beacon atwhich it is desired the apparatus become operative, say, a distance often thousand feet. This value may be termed the normal amperage of thesystem. Resistor |16 varies in resistance as the logarithmic sine of anangle, the purpose of the arrangement being that as far as resistance 16is concerned, the maximum current will ow when contact |15 is at centertap |11 and the current at other positions of contact |15 will bedecreased in according with the logarithmic sine of angle 0. Similarly,contact |14, cooperating with winding 10, will further reduce thecurrent of the circuit in accordance with the logarithmic cosecant ofAmmeter |84 has a logarithmic scale in units of distance and is socalibrated that the position of the ammeter needle will indicate thetrue distance to beacon N. Whereas, in the preferred form of ourinvention, the electrical calculating circuit in effect adds logarithmselectrically, in the present arrangement the calculating circuit ineffect subtracts logarithms electrically, the end being the same.

Fig. 18 is a duplicate circuit associated with the pointers L' and R' inthe same manner as the circuit shown in Fig. 17,` having prime numberscorresponding to numbers in Fig. 17. This duplicate circuit has,additionally, a movable resistor |86 controlled by a vertical-seekingdcvice, asbefore described (Fig. 13), the resistance being associatedwith a movable contact V|81 controlled by armature |08. Resistor |86will be recognized as corresponding to resistor I4 l, and contact |81 ascorresponding to contact |43 in Fig. 8. This duplicate circuit isarranged to have a minimum current corresponding to the maximum value ofthe sum of the four logarithmsV involved in the equation:

brated to read in units required, and corresponds to voltmeter |44 inFig. 10 just as ammeter |84 "in Fig. 17 corresponds to voltrneter |39 inFigs.

8 and 10.

Fig. 19, indicating an electrical arrangement for calculation in whichboth current and voltage are utilized, serves to further illustrate thescope of our invention. Battery |89 is shunted by resistor |90. 'Ihepositive end of resistor |90 is connected by wire |9| with a voltageterminal of indicating wattmeter |92, the other voltage terminal of thewattmeter being connected by wire |93 with a Contact |94 lmovable alongresistor |90. Battery |89 also energizes a parallel circuit throughresistor |95, a movable contact |96, wire |92a, the current coils ofWattmeter |92, and wire |9217 back to battery |89.

Battery |89 represents the base line of the triangle, resistor |90 iswound to vary as a desired function ofA one angle; and resistor |95 iswound to vary as the desired function of. another angle. Inasmuch as aWattmeter multiples current by voltage, it will be clear that the scalelof wattmeter |92 may be calibrated to read in units of the product ofthese factors. It will be 'noted that this arrangement multiplesdirectly, instead of, as in the case of the previous arrangements, byadding or subtracting logarithmic values and then translating the sum ofthe logarithmic values 'into an arithmetic product. In view of thedetailed explanations of the earlier described arrangement, it will beclear that a wattmeter asj` sociated with the arrangement shown in Fig.19

beacon and a second Wattmeter associated with a may be arranged toindicate distance to the -ing grounded at 202.

n to ow through the plate circuit of tube le.

in the lens system of the preferred form of our invention heretoforedescribed. .l

Such a diaphragm is omitted and a more simple lens system is used in asecond type of eye we have developed. This eye, by virtue of itsassociated control circuit, automatically centers a relatively largeimage, and, having centered the image, thereafter responds to minutedisplacements of the image from the desired central position. Suchresponse to minute displacements of the image is accomplished. as willbe further explained, by what may be described as electrically balancingthe energized areas of opposed cathodes in the eye.

The cathodes of an eye, in this second form of the pointer construction,are arranged as three spaced sectors of a circle, lx, 2x and 3x, asshown in Fig. 21, the corresponding areas of the lens of the pointer eyebeing indicated as Iy. 2y and 3y in Fig. 22.

The manner in which such a tri-cathode photoelectric eye contros anassociated pointer may, in view of the complete description of the firstform of our invention above, be readily understood by referring to thewiring diagram of Fig. 23.

Each eye is incorporated in a pointer construction in the same manner asheretofore described, reference being made to Figs. 3. 4 and 5 of thedrawings. This modification of our invention shows the use ofseries-wound motors to illustrate that either type of motor may be usedby employing a suitable relay arrangement.

In each photoelectric eye, cathode sectors Lr. 2a: and 3:1: have acommon plate 200, which plate or anode is maintained at a positivepotential by battery 20|. the negative pole of the battery be- Cathodesectors lx, 2x and 3.1:, respectively, of the photoelectric eye controlthe input circuits of corresponding amplifying tubes Iz, 2z and 32.

For example. current through the photoelectric eye affecting tube la maybe traced in the following circuit; ground 202. battery 20|,photoelectric plate or anode 200, cathode sector Ix, wire 203, band passfilter comprising condenser 204, and two parallel tuned circuits 205,wire 206 and ground 201. This circuit is tuned and filtered to themodulation frequency and controls the potential of grid 208 in tube la.

The three amplifying tubes are of the heater type, each having a heatingelement 209 suitably energized (source not shown), and cach having agrid-bias battery 2| 0. Current through photoelectric cathode la: willaffect the potential of grid 208, thereby causing a proportional currentIn similar manner. cathode 2x associated with grid 2|| controls theplate circuit of tube 2z, and

cathode 3x associated with grid 2|2 controls the plate circuit of tube32.

'I'he output circuits of these three tubes control two split-woundpolarized relays, relay 2|3 controlling the horizontal movements of thepointer, and relay 2|4 controlling the vertical movements of thepointer. The center tap of relay 2| 3 is connected by wire 2|5 to thenegative pole of battery 2|6, and the center tap of relay 2|4 isconnected by wire 2|`| to the negative pole o battery 2|8. Wire 2|9 .isconnected to plate 22d of tube Iz, plate 22| of tube 2a, and plate 222of tube 3e. Wire 2| 9 is connected to the positive pole of battery 2|6by Wire 223 and the positive pole of battery 2|8 by wire 224. Theendterminal in relay 2|3associated with the half of the relay coil markedRight, is connected by wire 225 to cathode 226 of tube Iz, and theAother terminal associated with the left portion of the relay coil, isconnected by wire 221 to cathode 228 of tube 2z. The end terminal inrelay 2|4 at the up side of the relay coil is connected by Wire 229 andwire 225 to cathode 226 of tube Iz, and the, opposite terminal of relay2|l| at the down end of the relay coil is connected by wire 230 tocathode 23| of tube 32.

Again, the terms right, left, up and down are used as occurring to aspectator viewing the pointer from the front.

Pivoted armature 232 of relay 2|3 is normally held at a central positionby a pair of opposed springs 2'33, and maintains its central positionboth when neither the right coil nor the -leit coil is energized andalso when both of the coils are equally energized. If the right coilalone is energzed, or, both coils being energized, if the right coilcarries the greater current, armature 232 will swing against contact234, thereby closing the circuit through wire 235, the right field inthe eld winding of the motor that controls the horizontal 'J movement ofthe pointer, wire 236, armature 231 of the motor,.wire 238,motor-energizing battery 239, and relay armature 232.

When the left coil of relay 2|3 alone is energized, or when both coilsof the relay are energized but the greater current flows through theleft coil, relay armature 232 will` swing against contact 240, therebyclosing a circuit through wire 24|, the left field of the motorcontrolling the horizontal movements of the pointer, wire 236, armature231, wire 238, battery 239, and relay armature 232.

Pivoted armature 242 of relay 2|4 is normally held in a central positionby opposed springs 243, and maintains its central position both whenneither the up nor down coil is energized and also when both coils areequally energized. When only the up vcoil is energized, or when, boththe up coil and down coil being energized, the more current flowsthrough the up coil, relay armature 242 will swing against contact 244,thereby completing a circuit through wire 245, the up field of the fieldwinding of the motor' that controls the vertical movements of thepointer, wire 246, armature 241 of the motor, wire 248, motor-energizingbattery 249, and relay armature 242.

When only the down coil of relay 2|4 is energized, or, both coils of therelay being energized, if greater current flows through the down coil,relay armature 242 will swing against contact 250, thereby closing thecircuit through wire 25|, the down iield of the motor controlling thevertical movements of the pointer, wire 246, armature 241, wire 248,battery 249 and relay armature 242.

In the arrangement being described, the total current through thephotoelectric eye is proportional to the total areas of the threecathode sectors energized by the image from the distant beacon, and* maychange with the size of the image in accordance with changes of distanceto the beacon. But the response of the pointerl itself, i. e., theaction of the two pointer motors,

depends upon the distribution of the energized areas among the threecathode sectors, the response being such that the pointer automaticallyseeks a position at which the energized areas are in equilibrium and atwhich the axi's of the pointer is directed at the distant beacon. It isapparent. then, that changes in the size of the An image appearing onthe periphery of a sector of the photoelectric eye will be caused totravel by a somewhat spiral path to a central position at which the sameproportion of the image will overlie each of the three sectors of thephotoelectric eye. The reaction of the pointer to an image on thepliotoelectric eye may be illustrated by considering what happens whenan image appears, for instance, at dotted position .252 as indicated inFig. 22. A current being set up across the plate circuit of amplifyingtube Iz, the right coil of relay 2|3 and the up coil of relay 2|4 willbe energized simultaneously, causing the pointer to move to the rightand up, thereby shifting the image left and downward at an angle offorty-iive degrees, as indicated by the arrow 253 of Fig. 22.

When the image first touches sector 2y there will be no change in themovement of the pointer because, while current controlled by tube 2zwill flow through the left coil of relay 2 I 3, that current will beless than the current flowing through the right coil of relay 2|3.Momentarily, at dotted position 254, the up coil, right coil and leftcoil will be equally energized. 'I'he right and left coils cancellingthe effect of each other, only the up coil will be eiective and theimage will move downward. Immediately thereafter, however, the greaterarea of the image will lie on the 2y sector, causing a greater iiow ofcurrent through the left coil than through the right coil, with theresult that the pointer will move up and left, causing the image to movedownward and to the right, as indicated by dotted line 255.

Since the image is moving at forty-five degrees from the vertical,whereas the line of division between sectors Iy and 2y is disposed atsixty degrees vertical, the image will clear sector 2y at position 256.As sector Iy is cleared, however, all relay coils except the left coilare deenergized and the image moves to the right into sector 2y again.The result is that the image progresses in the general directionindicated by dotted line 251, alternating between movements to the righttowards sector 2y and movements downward away from sector2y.

As soon as the image touches sector 3y at the dotted position 258, theimage Will move hori zontally to the right until a larger portion of itsarea overlies sector 3y than overlies sector 2y, at which time the imagewill turn diagonally upward to the right. Subsequently, the image willchange to movement vertically upward, followed by horizontal movement tothe left above the midpoint of the eye, and continue in the somewhatspiral path oi' progression to the center of the eye. While the imagedoes not move directly to the center of the eye, the response of thepointer is sufficiently rapid to complete the spiral within the shorttime interval required for the navigation of a rapidly flying plane.

A third form of pointer construction, shown in Figs. 24-29, is based onthe principle of bracketing the image of the beacon by a pair of eyes.One photoelectric eye 26| seeks the margin of the image at one side, anda second photoelectric eye 262 seeks the margin at the opposite side ofthe image, so that the pointer proper, a pivotally mounted rod 263mechanically held exactly midway between the two eyes, is continuouslydirected at the center of the image.

This combination of two photoelectric eyes and an intermediate pointeris pivotally mounted on a stub shaft 264 extending from fixed base 265.A lower gear 266 rotatably mounted on shaft 264 has a sleeve portion 261extending to the top of shaft 264. An arm 268 secured at its inner endto gear 266, as by screws, 269, carries at its outer end photoelectriceye 26|, the axis of the eye.

being radially disposed with reference to the axis of the shaft 264. Acollar 210 embraces sleeve 261 at the top and is provided with adepending arcuate ange 21|, for a purpose to be described later, theangular relation of ange 21| to arm 268., being fixed by virtue of a.suitable key 212 between the collar and sleeve 261. These members may beretained on shaft 264 by a suitable washer 213, the washer beingretained in turn by a nut 214 threaded to the reduced end 215 of stubshaft 264.

Pointer 263 is rotatably mounted on sleeve261, the pointer beingprovided with an integral sleeve V216 rotatably embracing the first;vmentioned sleeve 261 and extending upward to collar 210. A second collar211 keyed toth'ef'upper end of this second sleeve by key 218 isfintegralwith a radially extending contact arc 219. This contact arm terminatesin a downwardly extending finger 280. Rotatably mounted to sleeve 216between pointer arm 263 andcollar 211,'isa second and upper gear'28l forcontrolling the second eye 262. This eye, also radiallyl disposedrelative to the axis of shaft 264, is at the outer end of arm 282,secured to the gear as by screws 283.

263 will always bisect the angle between arms 268 and 282, 4so that ifeye-26| is directed 'at one edge of the beacon and eye 262 is directedat an opposite edge, the axis of pointer 263 will be directeti at thecenter of the beacon.

Journalled in a suitable bracket 281 are a worm gear 288 meshing withlower gear 266, and

worm gear 289 meshing with gear 28| (Fig. 27). Gear 288, controlling eye26| .is in turn controlled by motor 290, being connected therewith byshaft 29|. In a similar manner, motor 292 is connected byshaft' V293 toworm gear 289 to control the movements of eye 262.

To deenergize either motor, if it tends to move its associatedphotoelectric eye so far from the other eye as to make the pointerlinkage inoperative, and again, to deenerg-ize either, or both,

motors when the two arms are closed together inl the normal positionshown'in Fig. 25, certain mechanical switching arrangements arenecessary.

For such purpose, the previous identified arcuate flange. 21|,controlled by gear 266, overhangs upper -gear 28|.. Relative movement offlange 21| with respect to geary 23| in a direction to separate the twoeyes will; at a desired limit, deflect a flexible switch-member 294(Fig. 24) and relative movement in the opposite direction tending tobring the two arms together will, at a desired limit, deect a secondsuitably positioned flexible` switch-actuating member 295 (Fig. 25).Deection` of mex'ber 294 opens two switches, generally designated bynumerals 296 and 291. The construction of such a switch may be readilyunderstood by referring to Fig. 28, where it is seen that switch 296comprises a fixed contact 293 and -a second contact 299 mounted on mem-vWhen switch-member 295 is deected by the opposite end of flange 21|, aswitch generally designated 302 is opened, the switch comprising a iixedcontact 303 and a complementary contact 304 mounted on member 295.

It is apparent that contact arm 219, being virtually an extension ofpointer 263, will move with the pointer. An electric contact 305 ofsuitable construction is mounted on arm 219 to press continuouslyagainst a resistor -306, the resistor being curved concentric to theaxis of stub shaft 264. This resistor is wound to vary in accordancewith the functions or the logarithm of a function of an ang-le. Forexample, if this pointer construction is substituted for pointer L 'ofFig. 1, resistor 306 will be wound to vary as the logarithm of afunction angle p of the pointer with respect to the base line defined bythe two pointers on the airplane.

To prevent pointer contact 305 being carried past the ends of resistor306, means should be provided .to break the energizing circuits ofmotors 290 and 292 when the desired limits of pointer movements arereached. For this purpse, a flexible switch member 301 is positionednear one end of resistor 306 in a position to be deflected by theoverhanging end or iinger 280 of the pointer, and a similar exibleswitch member 308 is positioned near the opposite end of resistor 306.Deection of member 301 opens two switches, designated generally by thenumerals 309 and 3|0. Similarly, deflection of member 308 opens twoswitches, generally designated by numerals 3|| and 3|2.- Theconstruction of these switch mechanisms is similar to that shown in Fig.28.

It will be apparent that when the pointer assembly is in the normalclosed position, directed straight ahead, as shown in Fig. 25, switches296, 291,309, 3|0, 3|I, and 3|2 are in their normal closed positions,while switch 302 is in its normal open position.

Each of the two photoelectrlc eyes comprisesa suitable casing 3|3housing a lens system 3|4 at Athe front and a suitable photoelectriccell 3|5 at the rear, each photoelectric cell having cathode 3|6 and aring-shaped anode 3|1.

,Preferably the cathode of each eye is semicircular, as viewed'from thefront, and, in a pair of eyes, the cathodes are oppositely disposed, asindicated in Fig. 24, and, again, in Fig. 30, the latter figure showingdiagrammatically the disposition of three pairs of eyes on an airplaneas viewed from the front. In such an arrangement, each cathode takes inapproximately half the field of vision of an eye, so that a pair of eyeshaving complementary cathodes, as shown. will, together, cover theentire field of vision of one eye of the type shown in Fig. 6 or thetype shown in Fig. 22. To preclude any possibility of there being a gapin the eld of visin covered by the complementary cathodes, switch 302 isarranged to close only when the two cathodes are moved into definitelyoverlapping relation, such relationship being the normal relationship ofthe two eyes when not aiected by the distant beacon.

'Ihe electric circuits incorporated in this third form of pointerconstruction may be understood by referring to the wiring diagram, Fig.29. In either of the two eyes, 26| and 262, the circuit through thephotoelectric cell may be traced as i follows: negative pole of battery3|6, wire 3|9,

-photoelectric cathode 3|6, anode 3|1, wire 320, band pass ltercomprising'` condenser 32| and two parallel tuned circuits 322, wire323, and positive pole of battery 3|8.

An amplifying tube 324 is associated with eye 26|, and a similar tube325 is associated with eye 262. Grid 326 of tube 324 is connected to thephotoelectric anode side of the associated band pass filter and cathode321 of tube 324 is connected through grid bias battery 328 to theopposite side of the band pass filter.

In like manner, grid 329, of tube 325, is connected to the photoelectricanode side of the associated band pass filter, and Acathode 338 of tube325 is connected to the opposite side of the associated band pass lterthrough grid bias battery 33|.

Each of the amplifying tubes is a heater type,

having a heating element 332 energized from al suitable source (notshown).

Theplate circuit of tube 324 includes a suitable battery 333 and thesolenoid coil 334 of a relay that is generally designated by numeral335. Similarly, the plate circuit of tube 325 includes battery 336 andsolenoid coil 331 of a second relay generally designated by numeral 338.

v Armature 348 .of relay 335 carries two spaced insulated contactmembers 34| and 342. In the normal deenergized position of armature 348,contact member 342 is free of any contacts, and contact member 34|electrically connects spaced contacts 343 and 344. When relay 335 isenergized by current through coil 334, armature 348 moves contact member34| to a second position free of contacts 343 and 344, contact member34| in this second position electrically connecting a second pair ofspaced contacts 345 and 346. This same movement of armature 348, whenthe relay is energized, carries contact member 342 from its normal freeposition to a second position electrically connecting contacts 341 and348.

In` like manner, armature 349 of relay 338 carries two spaced insulatedcontact members 358 and 35|. When relay 338 is energized by currentthrough coil 331, armature 349 moves contact member 358 from a normalposition electrically connecting contacts 352 and 353 to a secondposition electrically connecting contacts 354 and 355, andsimultaneously moves contact member 35| from a normal position free ofall contacts to a second position electrically connecting contactmembers 356 and 351.

In describing this third form of pointer construction and its action,the words right and left will be used as occurring to a person lookingoutward over the pointer from a position at the rear. This direction ofreference isthe opposite of that suggested inconnection with thepreviously described forms of pointers, but is believed to favor clarityof explanation.4

Relay 335 controls the action of motor 298, thereby controlling themovements of the lower photoelectric eye 26|, covering the left half ofthe eld of vision; and relay 338 controls the action of motor v282,thereby controlling movements of upper photoelectric eye 262 responsiveto the right half of the field of vision. The armature and the split eldcoil of motor 298 are generally designated by numerals 358 and 359,respectively; and, on the other side of the diagram, the armature andthe split eld coil of motor 292 are generally designated. by numerals368 and 36|, respectively.

Contact 341 is connected to the left eld' of the motor associated witheye 26|, the connection being through. switches 296 and 3| I, previouslydescribed, the switches being in series. Contact 343, associated withleft relay 335; is connected to the right eld half of eld coil 359 ofthe same motor, the connection being through switch 389, previouslydescribed, and in series therewith, a second switch 362, the` purpose ofwhich second switch will be described later.

Contact 351, associated with right relay 338, is connected with theright field of the motor controlling the right eye 262, the connectionbeing through the two switches 291 and 3|8, previously mentioned, theswitches being in series. Contact 353 is connected to the left eld ofthe motor controlling the right eye 262, the connection being throughtwo switches in series, switch 3|2, previously mentioned, and a switch363, the purpose of which will be described later.

Connection is made from the center tap of field coil 359 of the motorcontrolling the left eye through armature 358 of that motor to contact345 of left relay 335. In a similar manner, connection is made from thecenter tap of iield coil 36| of the motor controlling the right eyethrough armature 368 of that motor to contact 354 of the right relay338.

Wire 364 interconnects contact 345 of the left relay and contact 354 ofthe right relay, and is connected to one terminal of motor-energizing.battery 365 by a branch wire 366, this branch wire being controlled byswitchV 382, previously described, (Fig. 24). The second terminal ofbattery 365 is connected to wire 361, which wire interconnects contacts344 and 348 of the left relay and contacts 356 and 352 of the rightrelay.

Suppose, the pointer and eyes being in the normal position shown in Fig.25, the airplane is approaching the distant beacon, the beacon being atthe left extremity of the combined field of vision of the two eyes 26|and 262. This image, energizing cathode 3|6 of the left eye at theselected modulated frequency, will cause the left relay 335 to beenergized, whereupon a circuit through the motor associated with theleft eye will be established as follows: battery 365, wire 361, contact348, contact member 342, contact 341, switches 296 and 3l|, left fieldof coil 359, armature 358, contact 345, contact member 34|, contact 346,back to battery 365. Motor 298 will cause eye 26| to move to the left,and the eye will continue to be so moved until the image passes over theinner straight edge of the semicircular cathode 3|6. This same actionmay be described as a movement of the eye towards the outside edge ofthe image of the distant beacon.

At the beginning of this leftward movement of eye 26|, switch 382 willautomatically close. Whenever relay 335 is deenergized while switch 382is closed eye 26| will move to the right because of the circuit: battery365, wire 366, switch 382, wire 364, motor armature 358, right field ofcoils 359, switches 389 and 362, contact 343, contact member 34|,contact 344, and wire 361 back to the battery. Therefore, as soon as eye26| moves sufliciently to the left to cause the image to traverse thecathode of the eye to a position clearing that cathode, the eye willautomatically reverse to the right. As a result of such an arrangement,left eye 26| will tend to hover at a position Where the straight edge ofits cathode will be approximately tangential to the left edge of theimage.

When switch 382 first closes at the beginning of the leftward movementof the left eye, the movement described above, the right eye will alsomove to the left following the rst eye, because of the followingcircuit: battery 366, wire 366, switch 382, wire 364, motor armature368, left field of 75 coils 36|, switch 3|2, switch 363, contact 353,contact' member 350, contact 352, and wire 331 back to battery 335. l

As soon as the right eye moves suiliciently to theleft to cause theimage to be positioned on its cathode, right relay 338 will be energizedand the eye willreverse tov the right because of y the followingcircuit: battery 365, wire 361, contact 356, contact member 35|, contact351,

switches 291 and 3| 0, right iield of coil 36 armature 360, contact 354,contact member 353, contact 355, back to battery 365. Because these lasttwo described circuits alternate, the iight eye will hover at a positionat which the straight edge of its cathode will be approximatelytangential to the image of the beacon, the eye being moved automaticallyto the left when the image does not touch the cathode and being movedautomatically to the right when the image does touchthe cathode.

Because each eye thus moves outward when energized and inward lwhendeenergized, it may -be said that the two eyes bracket" the image.

Whenever the beacon disappears from the iield of vision of the two eyes,the two eyes will automatically close together until switch 332automatically breaks the two motor circuits.

After a landing is made, the two eyes will usually come together and bedeenergized with the pointer directed to one side. For this and otherreasonsfit is desirable that there -be independent means convenientlyoperable by the pilot to move each pointer to a position straight ahead.For

this purpose, an auxiliary motor-energizing battery 369 (Fig. 29) isconnected by one terminal to wire 364, the other 4ten'ninal beingconnected to a switch 310. This switch is movable to one positionconnecting with wire 31| to the left iield of the motor controlling theleft eye, and is movable to a second position establishing connectionthrough wire 312 with the right field of the motor controlling the'right eye 262, the normal position beingl an intermediate neutralposition. Switch 310 is mechanically connected to switch 362 to openthat switch when connection is made with wire 31|, and is likewisemechanically connected to switch 363 to open that switch when connectionis made to wire 312.

` Suppose it is desirable to move pointer 263 to the left in order todirect it straight ahead. The

pilot will move switch 313 from the normalcen-4 cuit will cause eye 26|to move to the left, therener, if switch 310 is moved' to the right, acircuit will be closed as follows: battery 369, Wire 364,

A.armature 360, right eld of coil 33|, wire 312,

switch 313, back to battery 369. Switch 363 be.,

ing opened automatically when switch 310 connects with wire 312,energization of the left eld of coil 36| will be prevented.

Thisl third pointer construction has several advantages. It willaccommodate itself to an image of any diameter, the two eyes spreadingapart to accommodate the dimensions of the image while the pointerproper is automatically directed at the center of the image. The eyeconstruction itself is relatively simple, there being no criticalrelationship between cathode spacing in an eye and the size of theimage. It is important to note, also, that in the case of the previouslydescribed pointer constructions. the image may conceivably vibrate sofast across two opposed cathodes as to have the same eiect as aninordinately large image simultaneously overlying the two opposedcathodes. In `the case of the present construction, however, the twoeyes would automatically spread apart to the opposite limits of suchvibration, and the pointer, seeking the center of the range ofvibration, would thereby be directed to the center of the beacon. Afurther advantage of this third type of pointer construction is therapidity with which the pointer is centered on the beacon. In the otherconstructions, the pointers move circuitously to the Idesired positiondirected at the center of the image, whereas in the present constructionthe pointer-movement is more nearly direct, there being no diagonallines described by the path of the image. Another advantage is'that thearea of image necessary ,to establish an ei'- fective current throughthe eye is immaterial.

It is suggested that three pairs of such eyes be arranged on anairplane, as indicated by Fig. 30, showing the arrangement of the eyesas viewed from the front. 'Ihe pointer controlled by the pair of eyes onthe left wing, the pointer designated by numeral 313, will correspond topointer L of Fig. 1 and will, therefore, control contact |33 of Fig. 8.The pointer controlled by thepair oi.' eyes designated by numeral 314:on the extremity of the right wingof the plane corresponds to pointer Rof Fig. 1 and will, therefore, control contact |46, indicated in Fig. 8.The third pair of eyes 315 is mounted to bracket the image vertically toascertain angle of Fig. 2. The pointer associated with this third pairof eyes will. therefore, control contact '|43 of Fig. 8. It is apparentthat, with such a hook-up, the instruments designated in Fig. 8 willindicate the distance, altitude and course, afs previously described.

For the further guidance of the pilot, we nave devised a ground speedindicator. the construction of which may be understood by reference tothe circuit shown in Fig. 20.

Vacuum tube 316 is shown here as a batteryoperated screen grid tube,although other types may be employed. Filament 311 is heated by an Abattery 318,'the current being controlled by rheostat 319. In the usualmanner, screen 333 of the tube is connected to a central cell of Bbattery 38| by wire 332. Plate 333 of the tube is connected to ammeter334 by wire 335, the ammeter, in turn, being connected to the positivepole of battery 33| by wire 335 to complete the plate circuit.

The negative pole oi C battery 336 is connected to grid 331 of thi` tubethrough a relatively high resistance 338.

A n independent circuit comprises a suitable battery 339, shunted .by asuitable resistor 393l wound to varyfdirectly as the tangent of anangle. This resistor is provided' with a movable contact 39|, theconstruction of the resistor and contact being similar either to thatindicated by Figs. 11 and 12 or that shown in Figs. 24 and 25.

This contact is mechanically controlled by tential of contact 39| willalso vary directly as distance D.

Contact 39| is connected by wire 392 to grid 381 and, therefore, to thegrid end of resistance 388. A suitable condenser 393 is inserted betweenthe low potential end of resistor 390 and the neg-ative pole of Cbattery 386. It is suggested that the condensor have a capacity of onemicrofarad and that resistance 388 have a rating of 106 ohms, -if a timeconstant ofv approximately one second is desirable. It is apparent thatcharges on opposite sides of condensor 393 will balance at valuesdetermined by the position of contact 39| on resistor 390, and that anychange in the value of the balanced charges occasioned by a change inposition of contact 39| will cause a compensating ow of current throughresistor 388 for a duration of approximately one second.

This compensating current is dependent solely upon changes in potentialof contact 39|, dying away whenever the contact is stationary for morethan a second, and is directly proportional to the rate of such changesin the potential of the contact. .Now the potential of contact 39| atany given moment corresponds to distance D, as heretofore stated, and,therefore, the value of the compensating current through resistance 388is proportional to the rate of change of that distance, i. e., the speedwith which the ship approaches the beacon.

Ammeter 384 is indexed to serve as a speed indicator, being set to showzero speed at normal amperage in the plate circuit as determined bynormal potential of grid 381. As the airplane approaches the distantbeacon, angle p becoming progressively more acute, contact 39| movestowards the positive end of resistance 390, as indicated by the arrow,thereby causing compensating current to ilow from the contact throughresistance 388 to condensor 393. This transitory compensating current,by making grid 381 less negative, causes a proportionate increase in thecurrent through the plate circuit of `tube 316, so that ammeter 384,being properly calibrated, will 'indicate the instantaneous speed withwhich the airplane approaches the beacon.

It is true that the ammeter, strictly spreaking, does not measure theground speed, because distance D is measured in an air line at an anglefrom the horizontal, but this air line speed approximates ground speedso closely" that, for practical purposes, itis not deemed necessary tocomplicate the apparatus with further means to correct for the angle ofthe air line.

Having described our invention, we claim:

1. Apparatus for computing 4the distance between two points, comprising,in`combination: means generating electro-magnetic radiations from one ofsaid points, the otherbeing the receiving point; means at the receivingpoint for receiving said generated electro-magnetic radiation; twopointers associated with the receiving point spaced to denne aA baseline for computing distance by triangulation; means connected with eachpointer responsive to said electro-magnetic radiations to automaticallytrain each pointer on the source of the radiations; and meansoperatively connected to at least one of said pointers to automaticallyderive the distance between the two points from the angular dispositionof said pointers with respect to said base line.

2. Apparatus for computing the distance between two points, comprising,in combination: means generating electro-magnetic radiations from one ofsaid points, the other being the receiving point; means at the receivingpoint for receiving said generated electro-magnetic radiation; twopointers associated with the receiving point spaced to dene a base linefor computing distance by triangulation; means connected with eachpointer responsive to said electro-magnetic radiations to automaticallytrain each pointer on the source of the radiations; an electric circuithaving a variable energy characteristic determined by two factors, saidcharacteristic corresponding in value with the distance between the twopoints to be measured, said factors corresponding in value with factorsin an equation for computing the distance by triangulation; meansinterconnecting the pointers and circuit whereby the pointers controlsaid characteristic through at least one of said factors in accordancewith said equation; and means controlled by the circuit to indicate theinstant value of said characteristic, said means being adapted toexpress the Value as distance between the two points.

3. Apparatus for computing the distance between two points, comprising,in combination: means generating electro-magnetic radiations from one ofsaid points, the other being the receiving point; means at the receivingpoint for receiving said generated electro-magnetic radiations; twopointers associated with the receiving point spaced to define a baseline for computing distance by triangulation; means connected with eachpointer responsive to said electro-magnetic radiations to automaticallytrain each pointer on the source of the radiations; an electric circuit;at least one voltage-regulating means associated with the circuitcorresponding with two or more factors in a triangulation equation andadapted to vary the voltage of said circuit in accordance with saidfactors, one of said pointers being operatively connected to saidvoltage regulator; and a voltmeter in said circuit calibrated in unitsof distance.

4. Apparatus for computing the distance between two points, comprising,in combination: means generating electro-magnetic radiations from one ofsaid points, the other being the receiving point; means at the receivingpoint for receiving said generated electro-magnetic radiations; twopointers associated with the receiving point spaced to define a baseline for computing distance by triangulation; means connected with eachpointer responsive to said electro-magnetic radiations to automaticallytrain each pointer on the source of the radiations; an electric circuithaving a minimum voltage corresponding in value to the logarithm of aconstant in a. triangulation equation; at least one voltage regulator inthe circuit corresponding to a variable in said triangulation equationand ada;p ted to vary the voltage of the circuit above said minimum inaccordance with the values of the logarithm of said variable, one ofsaid pointers being operatively connected to said voltage regulator,whereby the instant voltage of said circuit corresponds to the instantvalue of the logarithm of the distance between said two points; andavoltmeter

